Temperature-responsive switch unit



United States Patent TEMPERATURE-RESPONSIVE SWITCH UNIT Howard A. Rike, Pasadena, Calif., assignor to Sentinel of Safety, Inc, San Carlos, Calif., a corporation of Nevada Application March 28, 1955, Serial No. 497,173

8 Claims. (Cl. 200-137) The present invention relates to temperature-responsive switches of the type known as thermostatic switches, such as are employed to close or open electric control circuits in accordance with predetermined temperature changes. More particularly the present invention relates to temperature-responsive switches of the type employed in fire detection circuits.

it is an object of my invention to provide a temperature-responsive switch unit that may conveniently be set up at its place of use and which may readily be connected into an electric circuit.

Another object of the invention is to provide a temperature-responsive switch unit, of the type referred to, that is of simple and inexpensive construction, and yet is highly sensitive and dependable in practical performance.

Still another object of the invention is to provide a thermostatic switch unit, of the type referred to, that may conveniently be assembled from simple and rugged component parts and when so assembled, protects the actual switch mechanism from atmospheric influences so that said mechanism may retain its setting, its sensitivity and its dependability for extended periods of time.

Yet another object of the invention is to provide a switch unit, of the type referred to, that may readily be pre-set to respond to a predetermined temperature level.

Furthermore, it is another and important object of the invention to provide a thermostatic switch unit, of the type referred to, that is adapted to respond to different ambient temperature levels depending on whether a rise in the ambient temperature occurs gradually or abruptly.

More specifically, it is an object of my invention to provide a thermostatic switch unit, for fire detection circuits, that is adapted to respond to a predetermined ambient temperature level whenever the ambient temperature rises gradually to said level, and which will respond to a substantially lower temperature level if the increase in ambient temperature occurs rapidly.

These and other objects of my invention will be apparent from the following description of the accompanying drawing which illustrates a preferred embodiment thereof and wherein:

Figure l is a vertical section through an assembled temperature-responsive switch unit constructed in accordance with my invention and specifically designed for operation as a fire detection unit;

Figure 2 is a vertical section, similar to Figure 1, through the outer shell or housing of the switch unit illustrated in Figure 1;

Figure 3 is a side elevation of the actual switch mechanism comprised in the unit illustrated in Figure l; and

Figure 4- is an enlarged fragmentary view of a vertical section through the lower end of the switch unit shown in Figure 1.

In the exemplary embodiment of the invention illustrated in the accompanying drawing, the actual switch mechanism of the temperature-responsive switch unit of my invention comprises two oppositely arched, juxtaposed spring struts 12a and 12b that face each other with 2,755,359 Patented July 17, 1956 "ice their concave surfaces as shown in Figures 1 and 3. The bottom ends of said spring struts, as viewed in said Figures 1 and 3, are bent backwardly to form barbs 14a and 14b, respectively (Fig. 4) by means of which the struts are securely anchored in transversely spaced relation within a cylindrical plug 16 of a suitable dielectric plastic. The opposite ends of the spring struts 12a and 1211 are embedded in spaced relation in another cylindrical plug 18 of a dielectric plastic and are bent outwardly to form connector lugs 20a and 29b, respectively, that project in diametrically opposite directions from the upper portion 22 of said plug 18 which is of a somewhat smaller diameter than the lower portion 24 thereof. At their midpoints the spring struts 12a and 12b carry on their confronting inner surfaces contact beads 26a and 26b, respectively, which are preferably made of silver. Embedded in the lower plug 16 near the bottom end thereof is the head 27 of a centering pin 23 whose stem 29 projects from the bottom face of said plug along the center axis thereof, as shown in Figures 1 and 3.

When the spring struts 12a and 12b are held under compression in the direction of the center axis of their mounting plugs 16 and 18, which tends to arch said struts outwardly away from each other, the contact beads 26a and 26b are separated and the circuit into which the struts may be connected by means of the lugs 20a and 20b is therefore interrupted. When the compression exerted upon the struts 12a and 12b is sufficiently relaxed, however, to allow them to straighten out, the beads 26a and 26b come into contact with each other which is effective to close the circuit into which the switch mechanism 10 is connected. The described automatic switch mechanism 10 forms in itself a unit that is of simplest construction, yet rugged and shock-resistant during manipulation and practical use, and which may be employed in devices other than the fire detector device to be described in greater detail hereinafter.

To maintain the spring struts 12a and 12]) under a predetermined degree or compression that maintains the contact beads 26a, 26b separated from each other under ordinary temperature conditions, the switch mechanism 10 is inserted into a thin walled cylindrical shell or housing 30 of a metal or metal alloy of high thermal conductivity and of a high thermal expansion eoefiicient, such as brass or stainless steel. The main body of the metal shell 30 is of such diameter as to snugly receive the lower dielectric plug 16 of the switch mechanism 19, while its upper end is somewhat expanded radially, as shown at 32, to form an annular shoulder 34 against which the lower, large-diameter portion 24 of the upper plug 18 may bear, while the upper portion 22 of said plug protrudes upwardly beyond the upper edge 36 of the metal shell 30 so that the connector lugs 23a and 2012 are disposed above and project radially beyond said upper edge. To firmly secure the upper end 24 of the switch mechanism 10 to the shell 30, a body 38 of a thermosetting dielectric plastic of relatively low heat conductivity yet high heat capacity, such as alkyd is moulded around the upper end of shell 10 and the outwardly protruding end of the plug portion 22 with the radially projecting connector lugs 20a and 20b in such a manner as to hermetically seal off said shell at its upper end. To provide for dependable connection between the plastic body 38 and the metal shell 30 the upper end of said shell may be knurled along its outer surface, as indicated at 39 in Figure 2. The plastic body 33 may take the form of a base as shown in Figure 1, by means of which the switch unit of the invention may be secured to the ceiling or the wall of a room or may be mounted upon shelf or table. Embedded in the base 38 at diametrically opposite points thereof and in contact with the connector lugs 20a and 2%, respectively, may be internally threaded metal plugs 40a and 40b which are engaged by screws 42a and 421), respectively, with which the leads of an electric circuit may be conductively connected to the spring struts of the switch mechanism 10. Settable means is provided to exert pressure upon the switch mechanism from the opposite end of the metal shell 30 so as to flex the spring struts 12a and 12b to a predetermined degree away from each other. For this purpose the lower end of tube 30 (as viewed in Figures 1, 2 and 4-) is closed, as shown at 44, except for an internally threaded central aperture 46 that is engaged by an externally threaded tubular bolt 48. The flat-topped head 50 of said bolt is disposed within the shell 30 and bears against the flat underside of the head 27 of pin 28 which head is embedded in the lower dielectric plug 16 as described hereinbefore, while the stem 29 of said pin is received within the center bore of the tubular screw bolt 48, as illustrated in Figure 4. The free end of the tubular bolt 48 is provided with a slot 52 which may be en gaged by a screw driver to adjust its vertical position within the threaded aperture 46 and in this manner preset the compression exerted upon the switch mechanism 10 which determines the distance between the contact beads 26a and 26b thereof under ordinary temperature conditions. Then, when the ambient temperature rises, the shell or case 30-which is made of a material of a high thermal expansion coeflicient as previously pointed outexpands and increases in axial length which relaxes the flexing pressure exerted upon the spring struts of the switch mechanism 10 since expansion of the shell 30 moves the pressure exerting bolt 48 away from the plug 16. This permits the spring struts 12a and 12b to straighten out under their own resiliency and under the elongating effect of rising temperature upon their structure until the contact beads 26:: and 26b meet and close the circuit into which the thermostatic switch of the invention is connected.

It will be apparent that the moment at which the beads 26a and 26b meet and establish conductive contact, may be preset at will within a substantial temperature range by appropriate adjustment of the tubular bolt 48 at the closed end of shell 30, and when a desired setting has been achieved, it may be rendered permanent by dropping solder into the aperture 46, as indicated at 54' in both Figures 1 and 4. This offers the added advantage of hermetically sealing the lower end of the shell so that the switch mechanism 10 is completely sealed ofi from the outside and is therefore protected from deterioration due to atmospheric influences.

I have found that by embedding one end of the shell or case 30 whose thermal expansion operates the switch mechanism 19, to a substantial extent into a relatively large body of a material of high heat capacity yet substantially lower heat conductivity than the material from which the shell is made, I achieve a highly desirable differential effect in the operation of the switch unit of my invention in that a rapid increase in the ambient temperature, such as an increase of from 30 F. to 40 F. per minute which is indicative of a true emergency, will cause the beads 26a and 26b to make contact with each other at a much earlier stage than a gradual temperature increase such as from 1 F. to 10 F. which may occur in the normal course of events and may not signify any real danger even though the ultimately achieved total increase in temperature might be considerable. I believe that this is due to the fact that, during a rapid increase of the ambient temperature, the body 38 of plastic material which is of a relatively low heat conductivity as compared with the material from which the shell 30 is made, is incapable of absorbing heat from said shell at a rate commensurate with the rate at which heat is absorbed by said shell from the ambient atmosphere so that the shell reaches rapidly the temperature level at which it permits closure of the contact beads 26a and 26b. On

the other hand, when the temperature increase is gradual, the plastic body 38 absorbs heat from the metal shell at a rate comparable with the rate at which it is imparted to said shell, and since the plastic body possesses substantial heat capacity, this is efiective to delay substantially a rise in the temperature of the shell to a point where the beads 26a and 26b come into contact with each other. Whatever the real explanation of the differential effect of a thermostatic switch unit constructed in accordance with my invention may be, said effect is highly desirable since it activates fire alarm devices and fire fighting equip ment controlled by the switch unit of my invention much sooner after a temperature rise commences than could otherwise be provided for without running the risk of setting ofi blind alarms under temperature variations that occur in the normal course of events.

This is a continuation-in-part of my copending U. S. patent application Serial Number 376,918, filed on August 27, 1953, for Thermal Actuator For Fire Alarm Circuits.

While I have explained my invention with the aid of an exemplary embodiment thereof, it will be understood that the invention is not limited to the specific constructional details illustrated and described, which may be departed from without departing from the scope and spirit of my invention.

I claim:

1. A thermostatic switch unit comprising a switch mechanism, a thin-walled, elongated housing of a metal of a high heat-expansion coefiicient surrounding said switch mechanism and arranged, upon thermal expansion, to actuate said switch mechanism, and a relatively large body of a dielectric material of relatively low heat conductivity and relatively high heat capacity surrounding a minor portion of said housing in thermally conductive contact therewith.

2. A thermostatic switch unit comprising a switch mechanism having two oppositely arched juxtaposed spring struts and opposed contact beads provided on the confronting surfaces of said struts, an elongated thin- Walled housing of a metal of a high heat-expansion coefiicient surrounding said switch mechanism and arranged, upon thermal expansion, to actuate said switch mecha nism and a relatively large body of a dielectric material of relatively low heat conductivity and relatively high heat capacity in the form of a mounting base surrounding one end of said housing in thermally conductive contact therewith. v

3. A switch mechanism for a thermostatic switch unit comprising a pair of oppositely arched, juxtaposed spring struts, opposed contact beads provided on the confronting surfaces of said struts, and plugs of dielectric material encasing the adjacent ends of said struts and maintaining them in a spaced electrically insulated relation.

4. A switch mechanism for thermostatic switch units, comprising a pair of oppositely arched, juxtaposed spring struts, contact beads provided at the mid points of said struts on the confronting surfaces-thereof, and cylindrical plugs of a dielectric material encasing the adjacent ends of said spring struts and maintaining them in spaced relation, the strut ends in one of said cylinders being bent outwardly to project radially from their respective plug of dielectric material.

5. A thermostatic switch unit comprising a pair of oppositely arched juxtaposed spring struts having contact beads on their confronting surfaces, a thin metal shell surrounding said spring struts, a base of a dielectrical material of low heat conductivity surrounding one end of said shell and maintaining the corresponding ends of said spring struts in fixed relation with regard to said shell, a plug of dielectric material encasing the opposite ends of said struts and slidably received within said shell, and means at the end of said shell opposite to said base settable to exert a predetermined degree of pressure upon said slidable plug to flex said struts apart to a predetermined extent under ordinary temperature conditions.

6. A thermostatic switch unit comprising a pair of oppositely arched spring struts disposed side by side with their concave surfaces facing each other and having contact beads at the midpoints of said concave surfaces, a thin elongated metal shell of a high thermal expansion coefficient surrounding said spring struts, a relatively large body of a dielectrical material of low heat conductivity and high heat capacity in the form of a mounting base surrounding one end of said shell and main taining the corresponding ends of said spring struts in fixed relation with regard to said shell, a plug of dielectric material encasing the opposite ends of said struts and slidably received within said shell, and means at the end of said shell opposite to said base settable to exert a predetermined degree of pressure upon said slidable plug to flex said struts and hold said beads a predetermind distance apart under ordinary temperature conditions.

7. A thermostatic switch unit for fire detection circuits comprising a pair of oppositely arched juxtaposed spring struts, contact beads provided on the confronting surfaces of said struts, a thin metal shell surrounding said struts, means holding the adjacent ends of said struts at one end of said shell in fixed relation to said shell, a plug of a dielectric material encasing the 0pposite ends of said struts and slidably received within said shell, and a screw bolt threadably received in the corresponding end of said metal shell and having a head within said shell in contact with the outer face of said slidable plug, said screw bolt being operable to exert pressure upon said slidable plug to flex said spring struts to a predetermined degree under ordinary temperature conditions.

8. A thermostatic switch unit for fire detection cir cuits comprising a pair of oppositely arched spring struts juxtaposed with their concave surfaces facing each other, contact beads provided at the midpoints of said concave surfaces, a thin cylindrical metal shell surrounding said spring struts, dielectric means holding the adjacent ends of said struts at one end of said shell in electrically insulating spaced relation to each other and in fixed relation to said shell while sealing said shell end hermetically, a plug of a dielectric material encasing the opposite ends of said struts and slidably received within said shell, the respective end of said shell being contracted to form a small threaded aperture, a screw bolt threadably received in said aperture and having a head within said shell in contact with the outer face of said slidable plug, said screw bolt being settable to exert pressure upon said slidable plug to flex said spring struts to a predetermined extent under ordinary temperature conditions, and means holding said screw bolt in set position and hermetically closing said aperture.

References Cited in the file of this patent UNITED STATES PATENTS 1,392,340 Lane Oct. 4, 1921 1,501,019 Lippincott July 8, 1924 2,257,990 Turenne Oct. 7, 194-1 2,307,867 Smith Jan. 12, 1943 2,373,857 Smith Apr. 17, 1945 2,389,103 Wood Nov. 13, 1945 

